Bulk material, such as concrete, is known to be brittle with low tensile strength, and may crack under low strains. Concrete, as an example, may be reinforced, such as with steel reinforcing bars or discrete fibers to provide post cracking tensile capacity. Such fiber reinforced concrete may include hydraulic cement, water, aggregates, and short, randomly distributed discrete fibers. Discrete fibers can be used to control cracking behavior, improve impact resistance, and improve toughness of concrete. Discrete fibers can increase mechanical properties of concrete by intersecting and transferring load across cracks. Discrete fibers can also increase concrete's resistance to early age plastic shrinkage cracking by increasing strain capacity of fresh concrete.
The ability to transfer loads across cracks is impacted by a fiber's pullout resistance.
Components affecting pullout resistance include physical or chemical adhesion, friction, mechanical anchorage or fiber-to-fiber interlock. To increase pullout resistance, conventional fibers have used mechanical anchorage via hooked, turned ends or dumb-bell shaped ends, or undergo chemical modification to form a chemical bond with the concrete matrix itself. Conventional manufacturing techniques for polymeric fibers include post extrusion steps of fibrillation, crimping and embossing of surfaces to improve the fiber-matrix bond. Such techniques require additional and costly manufacturing steps to impart these surface modifications to the fiber after extrusion of the fiber itself.
Accordingly, there exists a need for a method to produce a fiber with increased pullout resistance by a simple and inexpensive modification to the fiber.